Pi, represented by the Greek letter π, is of course the ratio of the circumference of a circle to its diameter, and is also the ratio of a circle’s area to the square of its radius. Ever so versatile, the number π is used in all kinds of maths. Geometry and trigonometry obviously, but also calculus, physics, statistical probability and even chaos theory.

Celebrated in song and poem, there was even a movie called Pi about a number theorist who tried to understand the entire world through numbers and ended up drilling a hole in his head (an impulse I’ve often shared during my career working with computers.)

(Click image for a larger version.)

So do something today in celebration of the wonder of π. For Aussies, a meat pie for lunch would be fitting. You could order a pizza (sometimes called a pie), set your desktop wallpaper to the image above, read up about Pi on wikipedia, try and memorise the digits of π (the world record is 42,195 digits), or just run around in a circle like we do most days.